Interconnect systems, which are generated by an ultrasonic bonding process, for surfaces of active power semiconductor dies typically include a heavy aluminium wire bonded to aluminium metallization disposed on the die surface, or a heavy copper wire bonded to copper metallization disposed on the die surface. Attempts have been made to bond aluminium-coated copper wires to power semiconductor dies which have standard aluminium metallization. However, due to the hard copper core of such wires they sink into the aluminium metallization of the die during the ultrasonic bonding process and damage the active device area below the aluminium metallization.